Turbomachines include a rotational shaft known as a rotor and a stationary portion known as a stator. Turbomachines include, but are not limited to steam turbines, gas turbines, electrical generators, compressors, and pumps. For example, an electrical generator typically includes main components like a rotor and stationary electrical conductors. The rotor typically includes rotor electrical conductors that produce a magnetic field when energized with an electric current.
The rotor of a generator receives the energizing current from an energizing device coupled to an end of the rotor. The rotor typically contains conductors that mate to the energizing device and route the energizing current along the rotor axial centerline via an axial conductor. A radial lead conductor then routs the energizing current radially from the rotor centerline to the rotor surface where the energizing current is then directed to the magnetic field generating conductors.
If the energizing current is direct current, then the magnetic field produced is constant in magnitude. However, as the rotor rotates, the field strength at a stationary point will vary as the magnetic field poles pass by. The stationary electrical windings surround the rotor and are arranged to intersect the rotating magnetic field such that an alternating current is induced in the stationary electrical windings. The stationary windings are connected to an electrical network such that the induced alternating current is distributed to many users.
Operation of the generator produces heat within the internal components of the generator. Typically, generators are cooled by a cooling medium, such as air, water or hydrogen gas. In the case of hydrogen gas, care must be taken to prevent mixing of the hydrogen gas with the surrounding air to avoid an explosive mixture of hydrogen and oxygen. Typically, hydrogen cooled generators are operated under positive pressure and high hydrogen purity to ensure that a combustible mixture of hydrogen and oxygen does not result within the generator. A hydrogen cooled generator is typically enclosed within a strong shell-like frame that supports the weight and operational and transient loads of the generator, and also contains the hydrogen gas and prevents it from escaping into the atmosphere where it can form a combustible mixture.
In order to prevent a hydrogen gas leak path along the radial lead conductor, the conductor is sealed against surrounding structures. One means of sealing against hydrogen gas leakage is to employ deformable seals stacked around the radial lead conductor, thereby forming a gas tight barrier between the radial lead conductor and the rotor body. The deformable seals are compressed by a radial lead nut that surrounds the radial lead conductor and threads into the rotor body. The axial compression of the seals causes the seals to expand radially, forming a gas tight seal against the surrounding rotor structure. The compression of the deformable seals is critical to maintain proper sealing during operation. The amount of compression of the seals is determined at assembly of the rotor by the extent that the radial lead nut is threaded into the rotor body. In order to preserve the correct compression of the deformable seals, the radial lead nut should advantageously be restrained from further rotation, either clockwise or counter clockwise, with respect to the rotor body.
Typically, to prevent undesirable rotation of the radial lead nut, a portion of the rotor body is deformed into the radial lead nut using a blunt tool such as a punch and a hammer. The hammer is used to impact the tool to plastically deform a portion of the rotor body into the threads or receiving slots of the radial lead nut, thereby binding the radial lead nut and preventing unwanted rotation. Deforming the rotor body material into the radial lead nut to prevent rotation is a well known process known as staking. However, the deformed rotor body material resulting from staking can lead to undesirable stress risers and crack initiation sites.